Bugfixes:

- rename markdown -> gfmarkdown to avoid name clash causing notebooks to fail
- strip of .md suffix to make links work
use separate parameters to avoid mess
support quick doc access via sgtb.eu
tolerate SG prefix
update news
don't die if notebook dir is not available
update slogan for 3.1.0
add tool to convert latest NEWS entry
update news
update slogan
fix typo in slogan
Update GSoC text on the home page